1. Technical Field
The present invention relates to a electric vehicle having a drive wheel which is driven by a traction electric motor, a brake command device which can be operated by a driver, a brake releasing unit which is driven by supplying electricity, a brake shaft, and a friction plate.
2. Related Art
In the related art, a motor-driven structure in which a drive wheel which is a vehicle wheel is driven by a traction electric motor is considered in vehicles such as ground work vehicles having working machines driven for ground work such as lawn mowing and tilling, carriage vehicles such as golf carts used in golf courses, and service vehicles for transporting a plurality of passengers. A electric vehicle which is a vehicle driven by an electric motor is considered to be effective in view of energy conservation and environmental protection.
For example, as the ground work vehicle, a lawnmower vehicle is known which is equipped with a lawn mower which is the working machine, in which a worker rides on the vehicle and executes running of the vehicle and operation of the lawn mowing on the vehicle, and which is capable of self-running, and is called a ride-on lawnmower vehicle. As the lawn mower, for example, a lawn mowing rotary tool or the like is known. As the ride-on lawnmower vehicle, a structure may be considered which comprises a hydraulic pump which is driven by an engine, a hydraulic motor which is driven by the hydraulic pump, a drive wheel which is driven by the hydraulic motor, a motive power transmitting mechanism which transmits a motive power between the hydraulic motor and a drive wheel, a brake pedal which is a brake command device which can be operated by a driver, and a braking mechanism which blocks transmission of motive power from the hydraulic motor to the drive wheel by the motive power transmitting mechanism and brakes the drive wheel based on an operation of the brake pedal.
During the operation of such a lawnmower vehicle, when the driver operates on, that is, depresses, the accelerator pedal which is an acceleration command device, the hydraulic motor is driven and the drive wheel is driven. When the accelerator pedal is put on a non-operation state, that is, an OFF state, or the amount of depression of the accelerator pedal becomes 0, the amount of exhaust of the hydraulic pump becomes 0 and a braking force is applied on the hydraulic motor, resulting in braking of the drive wheel. In addition, when a large braking force is required such as a case when the vehicle is to be stopped on an inclined surface or a case when rapid braking is required, the driver depresses the brake pedal such that the braking mechanism is actuated and the drive wheel is braked.
If, on the other hand, an electric motor can be used in place of the hydraulic motor in this lawnmower vehicle, the equipment of the engine and the hydraulic pump in the vehicle becomes unnecessary, and there is a possibility that the space can be conserved and the energy can be conserved. However, a simple replacement of the hydraulic motor with the electric motor would result in a behavior of the vehicle different from that in the case of the hydraulic motor driven vehicle when supply of electricity to the electric motor is stopped, and consequently, an uncomfortable feeling for the crew.
For example, when the wheel is driven by the driving of the hydraulic motor, even when the engine is stopped and the supply of hydraulic pressure to the hydraulic motor is stopped, a braking force is generated by the hydraulic motor during running of the vehicle by the resistance of the oil in the hydraulic motor. In addition, even when the vehicle is parked on a slope, the engine is stopped, and the operation of the hydraulic motor is stopped, the oil in the hydraulic motor causes a resistance, and the vehicle does not tend to slip downhill on the slope. Even if the vehicle slips downhill on the slope, the vehicle can be stopped by the driver depressing the brake pedal or operating a side brake for maintaining the braked state of the drive wheel. However, the vehicle slipping significantly downhill during non-operation of the brake pedal or side brake is not preferred because an uncomfortable feeling may be caused for the driver.
On the other hand, if the hydraulic motor is replaced with the electric motor in the hydraulic motor driven vehicle described above without any special consideration, there is a possibility that the vehicle can be driven by the driving force of the electric motor and that that the drive wheel can be braked by operating on the brake pedal during braking. However, when the supply of electricity to the electric motor is stopped by, for example, switching the main power supply switch OFF or a sudden failure of a circuit including the power supply, unlike the hydraulic motor driven vehicle, the electric motor does not become a resistance, and the braking force would not act during the running of the vehicle. Because of this, when the brake pedal is not operated, the vehicle continues to run by inertia. In addition, when the power supply switch is switched OFF in a state where the vehicle is parked on a slope, because the supply of electricity to the electric motor is stopped, there is a possibility that the vehicle will slip downhill during the non-operation of the brake pedal or the side brake. Thus, there is a possibility that simple replacement of the hydraulic motor with the electric motor may cause an uncomfortable feeling for the driver with regard to the behavior of the vehicle.
JP 2002-178896 A discloses a golf cart comprising an engine, front wheels and rear wheels, and a transmission case for transmitting motive power from the engine to the rear wheels. In this golf cart, the four wheels including the front and rear wheels can be simultaneously braked by two systems of a manual operation and an automatic control. In addition, a brake is applied by pressing a brake pad against a brake drum or a disc brake plate, and the brake pad is made to act in the braking direction by pulling of a brake cable. Moreover, a case with a built-in deceleration mechanism with a brake clutch is placed on an output side of the electric motor functioning as an automatic brake actuator, and an arm fixed on one of output shafts protruding from the case and a brake releasing arm are connected by an interference connection mechanism. A pipe for manual operation and a pipe for automatic operation are rotatably fitted on a main axle placed at a lower side of the vehicle and extending in a vehicle width direction. In a state where the motor is reversely rotated for a certain amount, the pipe for manual operation is rotated in the counterclockwise direction by a biasing force of a biasing spring, and all of the front and rear wheels are braked. On the other hand, when the motor is normally rotated and the arm is rotated in the counterclockwise direction, the pipe for automatic operation is rotated in the clockwise direction against the biasing force of the biasing spring and the pipe for manual operation is rotated in the clockwise direction, resulting in releasing of the braking of the front and rear wheels. When the main switch of the golf cart is in the OFF state, an electromagnetic solenoid is switched OFF, the brake clutch is disconnected, the force from the electric motor does not act on the output shaft, and the output shaft becomes free. Consequently, the braking force acts on the front and rear wheels due to the biasing spring, and the parked state of the vehicle is maintained.
In the case of such a golf cart as described in JP 2002-178896 A, because the wheel is driven by the engine, when the engine is stopped during running, if the motive power transmitting mechanism which transmits the motive power from the engine to the wheel is connected, the braking force would act on the wheel. In addition, even when the engine is stopped during parking of the vehicle on a slope, if the motive power transmitting mechanism is connected, downhill slipping of the vehicle can be prevented. Such a reference does not disclose a structure for reducing the uncomfortable feeling for the driver with regard to the behavior of the vehicle when supply of electricity is stopped in a electric vehicle in which the drive wheel is driven with the traction electric motor.